1. Technical Field
The present invention relates to a developing device that develops an electrostatic latent image on a latent image carrier with a developer and an image forming apparatus.
2. Related Art
An electrophotographic recording type image forming apparatus that forms an electrostatic latent image based on image data on a surface of a latent image carrier by exposure is known. In the image forming apparatus, an image is formed by developing the electrostatic latent image with toner by a developing device and transferring the toner image on the surface of the latent image carrier onto a recording medium, such as recording paper. In recent years, such type of image forming apparatus is generally designed such that a toner cartridge, which is formed as one body with a developing device or separately from the developing device and which contains toner therein, is detachably mounted. When the contained toner is consumed by repeatedly developing an electrostatic latent image on a surface of a latent image carrier, toner for developing the electrostatic latent image on the surface of the latent image carrier is filled up by replacing the toner cartridge.
In such a developing device, the charging ability of toner deteriorates since the toner in a development chamber is stirred for a long time by a stirring member, a toner supply roller, and a regulation blade. When new toner and deteriorated toner remaining in the development chamber are used in a state where the new toner and the deteriorated toner are stirred to be mixed in the development chamber by replacement of a toner cartridge, the new toner with the high charging ability is selectively charged and charging of the deteriorated toner becomes insufficient. As a result, since the charged amount of the whole toner that is stirred to be mixed is not sufficient, regulation passing failure or adhesion (fogging) onto a non-image area occurs. In order to prevent this, JP-A-2000-181216 discloses a technique for processing of toner remaining in a development chamber. In this technique, a driving time of a developing device is counted, forcible writing is performed in a non-image area according to the driving time, and toner, the charging ability of which has deteriorated, within the development chamber is consumed.
However, in the known techniques, toner particles with different deterioration states (charging abilities) are mixed in the development chamber. Accordingly, regulation failure, fogging, and the like may occur because the toner particles with different charged amounts are mixed.